In order to achieve greater computer speeds and to miniaturize electronic devices, denser packaging of the active components becomes essential. However, such denser packaging is practicable only when the heat generated is speedily carried away from the active components. Frequently the components are mounted on a heatsink and are also enclosed by a cold cap. The major resistance to heat flow is generally in gaps. The gaps may be between the active component and the housing or between the active component and the heatsink or between the housing and the heatsink.
Prior thermal packaging compounds involved mostly resin or rubber based formulations which need curing or setting, such as curable polymeric resins. Such rubbery or rigid encapsulating materials may trap minute quantities of air at the interface and therefore may not provide effective thermal contact between the heat transfer surfaces. In addition, they are not easily removable to give accessibility to the active components, if necessary. Thermally conducting compositions have been made as exemplified by U.S. Pat. No. 3,885,984 to Wright and U.S. Pat. No. 4,265,775 to Aakalu et.al. The patent to Wright discloses a composition comprising a methyl alkyl polysiloxane and a thickener. The patent to Aakalu et al. discloses a composition including silica fibers. Generally, prior thermal compositions do not have high thermal conductivity and low viscosity for high solid loading and they may not be stable. European Patent 0114000 to C. Lien et al. also discloses a thermally conducting slurry. The particle size of the particles in the slurry is about 150 microns. In accordance with the European patent, there is solid liquid separation of the slurry. In fact, it is desirous for the particles to settle. Therefore, this composition is not stable.
Therefore, there still exists a need for a product which is stable, (over a few years), with regard to liquid separation and has high thermal conductivity and high electrical resistivity. This is difficult since normally those materials which have good thermal conductivity are also usually electrically conductive. In addition, there is a need for a product which will provide good thermal contact between the heat transfer surfaces and will accommodate different shapes and sizes of the circuit components.
Furthermore, there is a need for a compound which can be applied as a thin film. There is also a need for a compound which will withstand thermo mechanical variations encountered in electronic device applications without significant loss of its properties and finally there is a need for a compound which can be completely removed with common solvents to provide accessibility to the active components where necessary.